In recent years there has been a rapid development of “smart” tires, i.e. tires fitted with electronic systems that enable certain parameters to be measured, such as the inflation pressure, the temperature of the tire or forces exerted on the tire when it is rolling Such tires are also provided with electronic systems that enable the measurements so obtained to be transmitted to the vehicle on which the said tires are fitted. (For the sake of brevity the measurement and/or transmission systems, whether or not they be integrated in a casing, will be indiscriminately called “electronic units” in what follows.)
Such electronic systems are very often located inside the tire. They can be fixed directly onto the tire itself, for example in a pocket formed on an inside wall of the tire. Another way to fix an electronic system inside a tire is to use a “patch” which is stuck onto an inside wall of the tire (see for example the U.S. Pat. No. 6,782,741). A third possible approach is to attach the electronic system integrally to the inflation valve of the tire. The U.S. Pat. No. 6,278,361 describes a design in which sensors are arranged in a container which is attached to the valve. The present invention relates to this third approach.
Nowadays several types of valves are available, designed for very different uses. One type of valve which is fixed by clipping into place is known as a “snap-in” valve. In such valves the metallic tubular insert that encloses the actual valve mechanism is anchored in a valve body, for example made of rubber. The valve body has a peripheral groove to receive the edge of the rim hole. An example of a “snap-in” valve comprising an electronic unit is described in the U.S. Pat. No. 6,005,480 and illustrated in FIG. 4. Such an assembly has the advantage of being very compact, but it also has disadvantages. The volume available for the electronic unit is very small; moreover, since the electronic unit is rigidly connected to the valve, it undergoes all the valve's movements which can subject it to considerable stress. There is also the risk of destroying the electronic unit during the mounting and removal of the tire.
“Snap-in” valves are limited to inflation pressures not exceeding a certain threshold (typically 4.5 bar when cold) and are only suitable for rims of certain thicknesses as mentioned in the manuals of standards (ETRTO, TRA, etc.). In the context of passenger cars capable of reaching high speeds (i.e. above 210 km/h) it is preferable to use valves fixed onto the wheel rim by screwing (“clamp-in” valves): the valve body is introduced into the rim hole from the side of the rim corresponding to the interior of the tire when the latter has been mounted on the rim; the valve body is locked by a nut screwed onto the body from the other side of the rim. The valve base has an annular recess to accommodate an annular seal (O-ring, grommet, etc.).
It has been proposed to fit an electronic unit on such a valve. For example the U.S. Pat. No. 6,805,001 discloses an assembly formed by a valve and a sensor, the sensor being fixed on the valve by a mechanical articulation of the ball-and-socket joint type which enables the sensor to be adapted to the various rim profiles (see also FIG. 5). Another assembly of the same type is described in the U.S. Pat. No. 6,055,855. The disadvantage of such assemblies is that fitting them entails an extra screwing operation: besides screwing the valve onto the rim, the electronic unit has to be fixed on the valve in an optimum position relative to the rim. This operation makes the mounting process more onerous and increases its cost.
An improved assembly is disclosed in the U.S. Pat. No. 6,862,929. According to that document the sensor is fixed on a support comprising a valve contact wall, said wall being articulated elastically on the rest of the support (see FIG. 6). In contrast to the assemblies described earlier, this articulation does not require a specially adapted valve and ensures that the sensor is positioned as close as possible to the rim, without any need to adjust the sensor's position manually. Its disadvantage is that mounting is still relatively complex: the support has to be fixed onto the valve, for example by a screw as in the embodiment illustrated in FIG. 6. The presence of such a small fixing piece entails disadvantages, such as more complex mounting (the piece might be lost) and greater cost. The same drawback is found in still another assembly disclosed in U.S. Pat. No. 6,895,810.